Some apps use the Control and Option keys (the VO keys) together with another key to perform an action. If you’re using VoiceOver and want to use the app’s command, you can type a command that tells VoiceOver to ignore the next key combination.

Press VO-Tab.

VoiceOver will ignore the next key combination you press.

You can change many keyboard shortcuts for apps in the Keyboard Shortcuts pane of Keyboard preferences.